hyperframes lint: warn on [data-composition-id="<self>"] selectors that do not isolate per-instance #557

Summary

Until per-instance CSS scoping is fixed (see #556), block authors who follow the documented pattern [data-composition-id="my-comp"] { ... } will silently ship blocks that leak across sibling instances. A lint warning would catch this before it hits production rendering.

Suggested rule

For each composition file, parse its CSS (inline <style> and external .css referenced by <link>). For each rule whose selector contains [data-composition-id="<value>"] where <value> matches the file's own composition id (i.e., the value of data-composition-id on the root element):

• Warn (severity: warning, not error).
• Message: "Selector matches the block's own id; will leak to sibling instances when the block is embedded twice. Use #<id> for instance-isolated styling until per-instance scoping is supported (see Nested compositions: sibling instances share CSS scope under attribute selectors #556)."

Notes

• Severity should be warning, not error: there are legitimate cases where the author wants the rule to apply to all instances (e.g., truly global block styling).
• Keep silent when the selector targets a different data-composition-id value (legitimate cross-block targeting from a parent).
• Cross-reference real-world hit: https://github.com/sidorovanthon/anticodeguy-video-editing-studio file docs/operations/planner-pipeline-fixes/findings.md items D15/D21.

Related

• Nested compositions: sibling instances share CSS scope under attribute selectors #556 — Root-cause issue this rule guards against.
• Catalog block flowchart triggers HF lint rule template_literal_selector #559 — Existing lint rule template_literal_selector already catches a separate authoring issue in the same flowchart block; useful precedent for catalog-block lint gating.

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